[1] Yunnan Normal Univ, Sch Math, Kunming, Peoples R China
[2] Univ South Dakota, Dept Math Sci, Vermillion, SD USA
[3] Indian Inst Technol, Dept Math, Patna, Bihar, India
[4] Tamkang Univ, Dept Stat, New Taipei, Taiwan
[5] Yunnan Normal Univ, Sch Math, 768,Juxian Rd, Kunming 650500, Peoples R China